Impregnation of the grain side of leather with polysulfides



April 19, 1960 E. c. DOGLIOTTI ET AL 2,933,418

IMPREGNATION OF THE GRAIN SIDE OF LEATHER WITH POLYSULFIDES Filed Feb.4, 1959 Hes/L Side Legend:

Mat

Elasiomerz'c dep sizf' of organic polqsulfa'de polymer pluszefrqhydrafur/urql alcohol and or morpholine.

INVENTORS Eugene C-DOQZLOdi.

Joseph ClBcurg.

Charles 14/. Mam

ATTORNEY United States Patent IMPREGNATION (BF THE GRAIN SIDE OF LEATHERWITH PQLYSULFIDES Eugene C. Dogliotti, Sherborn, Mass, Joseph C. Barry,Woonsociret, RE, and Charies W. Mann, Framing ham, Masn, assignors tothe United States of America as represented by the Secretary of the ArmyApplication February 4, 1959, Serial No. 791,238

17 Claims. (Cl. 117-135.5) (Granted under Title 35, US. Code (1952),see. 266) The invention described herein, if patented, may bemanufactured and used by or for the Government for governmentalpurposes, without the payment to us of any royalty thereon.

This invention relates to the impregnation of the grain side of leatherwith polysulfides, and more particularly with the impregnation ofleather from the grain side with a. composition containing a liquidpolysulfide polymer and tetrahydrofurfuryl alcohol and/or morpholine.The leather thus impregnated possesses outstandingcoldweather-resistance and is resistant against the penetration of waterand petroleum and against attack by corrosive liquids; thus, footwear,handwear and other articles of clothing and equipment made from suchleather are highly useful for a variety of military and civilianpurposes, such as work in an open air motor pool or field maintenanceshop where the operator encounters varieties of climate, rain, spilledgasoline and oil, battery acid and other corrosive liquids.

Thus, a principal object of our invention is to provide a novel leathertreatment which is useful in impregnating the grain surface of leatherfor the purpose of resisting, from the grain side, the penetration ofliquids such as water, petroleum products, and corrosive type liquids,

such as battery acid.

Another object is the impregnation of leather with a material which whenintroduced into the interfiber space of the leather will permit thetreated leather to be serviceable at low temperature and will notadversely influence the durability and other desirable physicalcharacteristics expected of leather.

A further object of our invention is a preformed liquid compositiontreating agent containing as its principal ingredient a liquid alkylenepolysulfide polymer capable of being cured to form an elastomer, andtetrahydrofurfuryl alcohol and/ or morpholine as its other component(s),so as to make it possible to introduce the compositions into the leatherfrom the grain side and to effect a quick cure in the interfiber spaceof the leather.

A further advantage of our invention is a leather treating procedurewhich is simple, requires little time to perform, and can be carriedoutwith conventional equipment customarily on hand in commercialtanneries.

Other objects and advantages will be apparent from the followingdescription of our invention.

A leather impregnating composition for the purposes of our inventioncomprises a liquid mixture of from about 50 to about 80 parts by weightof a liquid alkylene polysulfide polymer capable of being cured to forman elastomer, and from about 20 parts to 50 parts by weight oftetrahydrofurfuryl alcohol or morpholine or a mixture oftetrahydrofurfuryl alcohol and morpholine. Depending on the formulaused, it may be desirable to add an effective amount of oleic acid,i.e., about A to about 2 parts by Weight per 100 parts by weight of thecomposition, to prevent an excessively fast and possibly uneven cure ofthe composition in the interfiber space of the leather. Representativeproportions of the principal components ice of our compositions inaccordance with our invention are: About, 50-75 parts by weight ofpolysulfide to about 25-50 parts of tetrahydrofurfuryl alcohol; or aboutparts by Weight of polysulfide to about 20-25 parts of morpholine; orabout 7580 parts by weight of polysulfide to about 20-50 parts of amixture of tetrahydrofurfuryl alcohol and morpholine.

These compositions may be prepared by simple mixing the ingredients insuitable proportions, depending on the type of leather being treated andon the degree of protection needed. The mixing may be'acco-mplished withthe undiluted materials or by employing a common solvent. Suitablesolvents include hydrocarbon solvents such as toluene or halogenatedsolvents such as perchloroethylene and thelike.

Representative suitable low molecular weight liquid polysulfide polymerswere found to have a molecular weight of about 1,000 to 5,000, and aviscosity of approximately 7 to 45 poises at 25 C. Such polysulfides arecommercially available from Thiokol Corp, Trenton, New Jersey, underdesignations such as Thiokol LP-32, Thiokol LP-2, Thiokol LP-33, andThiokol LP3. These polysulfides have polymer segments compose-d of anumber of formal groups linked by sulfur bonds and are terminated bymercaptan groups; some SH side groups may also be present in the chainor repeating formal units and some chain segments may also becross-linked at various points. Thus, the average structure of ThiokolLP-32 may be represented as a characteristic feature of the repeatingunits of these thiokols is the presence of alkylene groups, such as -C HHowever, it will be understood that the practice of our invention is notlimited to the Thiokols enumerated above, but that other alkylenepolysulfides may successfully be used instead.

Without limiting ourselves to any particular theory we ascribe theefficacy of tetrahydrofurfuryl alcohol and/or rno-rpholine in thepractice of our invention to their favorable solvent characteristics,absence of toxic eifects, and low flammability. In addition to theirsolvent action on and compatibility with the alkylene polysulfide,tetrahydrofurfuryl alcohol acts as a copolymer, and morpholine as acuring agent. The optional addition of a small amount of oleic acidserves to control the speed of the reaction and to prevent a runawayreaction; this, however, can also be accomplished by careful control ofthe reaction conditions even without the use of oleic acid.

We generally carry out the impregnation of leather in accordance withour invention by applying the liquid polysulfide polymer impregnatingcomposition to the grain surface of the leather. The treatingcomposition may be applied to the leather by any suitable manner such asrolling, swabbing, spraying or brushing. Shortly after application,during the mild to moderate heat curing operation preferably at about-160" F., say for 15 minutes to two days, a permanent polymeric barrierforms within the upper strata of the protein lattice of the leather.Polymer penetration into the leather is completely accomplished with theresult that the appearance and feel of the leather remains substantiallythe same as for untreated leather. Strength characteristics of theleather are not decreased by the treating process and indications arethat an improvement in some strength properties, e.g., abrasionresistance, are achieved. Leather comfort characteristics, e.g., watervapor permeability in the treated leather are adequate for use inhandwear or footwear.

'These results are in sharp contrast to leather dipped into the treatingcomposition so that polymer penetration into the leather occurs from theflesh side as well as the grain side. In the latter case the leather, topossess good liquid resistance, will be too stiff for use, especially atlow temperatures and the flesh side will not possess good feel and will.have lost most, if not all, of its ability to absorb perspiration.

Satisfactory results are attained when the impregnated leather containsfrom 12 to 20 grams of polysulfide polymer per square foot of leatherfor light leathers such as glove or garment type. Shoe upper leatherrequires more of the polymer in order to achieve good results,approximately 20-30 grams of polymer per square foot of leather. Ingeneral, l-18 grams of polymer are preferred for glove or garmentleather while 24-30 grams are best for shoe upper leather. Ordinarily,one application sufiices for glove or garment type leathers; while twoapplications may be found necessary in some cases for shoe upperleather.

Leather impregnation in accordance with our invention improves theliquid penetration resistance of many types of tanned leather, as, forexample, leathers tanned by mineral tannages such as chrome, zirconium,etc.; leathers tanned by vegetable tannages, such as chestnut, and bymixtures of vegetable tanning extracts comnionly used in the leatherindustry; leathers tanned by a mineral or vegetable material followed bya vegetable or mineral retannage; leathers tanned by synthetic typetannages, such as glyoxal or succinaldehyde; and the treatment isapplicable to leather prepared from any type of animal hide or skin,such as cowhide, horsehide, sheepskin, deerslcin and the like.

The accompanying drawing shows an enlarged edge view of a piece ofleather impregnated from the grain side in accordance with ourinvention, the penetration of the interfiber space of the leather by thepolysulfide being diagrammatically indicated by dots.

TESTS In the following examples, the water and gasoline resistances ofthe leather were evaluated as follows:

Water resistance was measured by the Quartermaster tap testerillustrated and described on pages 637 and 638 of the December 1956issue of Journal of the American Leather Chemists Association. Itconsists essentially of a rotating anvil which provides a uniform wetsurface, an arm and hammer which provides a definite force per unit areaon the leather specimen and a cam mechanism for lifting and releasingthe hammer, thus allowing it to fall on the anvil. During each strokethe fall of the hammer causes the mounted leather specimen to strike thewet anvil and thus exert a force or' strain on the fibers. in addition,the grain side of the specimen rubs against the rotating wet anvil underpressure until the cam lifts the arm. A tapping and rubbing action isthus repeated with each cycle (75 cycles per minute). Penetration of thewater completes an electrical circuit through the arm and rotating anvilto sound a buzzer, thus providing a well defined end point of the test.A one-half pound load is generally employed for glove or garmentleathers while a two pound load is generally used for upper leather. Ahammer drop distance of /z-inch is used for all leathers.

The Maeser water penetration machine is illustrated and described onpages 401 and 402 of the August 1947 issue of Journal of the AmericanLeather Chemists A..- sociation. The tester employs the principles oftesting for water penetration rate as specified in Method 8021 (datedJanuary 19, 1953) of the Federal Specification, Leather: Methods ofSampling and Testing, KK-L- 311a, dated June 26, 1956.

The apparatus consists of two V-shaped clamps with wedges that hold thespecimen in the position of a V- shaped trough so that it can beimmersed in water without leakage between the clamps and the leather.One clamp is fixed while the other is attached to an eccentric that ispowered by a motor. On rotating the eccentric the leather is flexed in amanner simulating service conditions. The apparatus is equipped with anadjustable water tank so that the lowest point of eachclamp isapproximately one inch below the surface of the water. A counter recordsthe number of cycles through which the specimen is flexed. Specimenis-flexed approximately cycles per minute. Following clamping of theleather specimen with the grain side exposed to the water, the specimenis flexed until the first appearance of water inside the leather troughis observed. The number of cycles is then read and used to represent thedegree of water resistance possessed by the leather.

Gasoline resistance was measured by determining the time required forpenetration of gasoline through a leather specimen rubbed with a rubbercovered finger. The specimen is placed grain side up on a paper towelresting on a fiat surface. Approximately 1 ml. of gasoline is pouredonto the grain surface and rubbed vigorously with the rough surface ofthe rubber finger. The specimen is lifted after 30 seconds, 1 minute and2 minutes to see if penetration and staining of the absorbent paper hasoccurred. The penetration time and corresponding ratings are as follows:

Penetration time, minutes Rating Below 0.5 Poor. 0.5 to 1.0 Fair. 1.0 to2.0 Good. Above 2.0 Excellent.

Pertinent evaluation of other leather properties were generallyperformed in general accordance with methods specified in FederalSpecification KK-L-Zilla.

We now proceed to describe the practice of our invention by means ofseveral specific examples, without, limiting ourselves to any details ofoperating conditions or specific proportions set forth therein.

Example I There was employed a leather treating composition containing57 parts by weight of Thiokol LP-32 and 43 parts by weight oftetrahydrofurfuryl alcohol.

Thirty sides of degreased chrome tanned cowhide garment leather weretreated in a tannery with the above composition using a 7" mohair paintroller to manually spread the material over the grain surface of theleather. Approximately one fluid ounce of the material was applied persquare foot of leather. Within 15 minutes after treatment, each treatedside was conveyed through a drying tunnel at Mil-160 F. for 15 minutes.After all sides had been passed through the tunnel once, and in a fewcases twice, depending on the amount of impregnating material remainingon the grain surface, they were placed in a drying loft overnight atapproximately 90- F. The dried leathers were then washed, fatliquored to4% oil, dried and staked.

Water and gasoline resistance was determined on leather specimensremoved from four areas of the side: the backbone-tail, thebackbone-center, belly-center, and shoulder. Ten of the thirty sideswere used in the evaluation studies to give 40 leather test specimens.Duplicate water resistance measurements were made on all specimens Whilegasoline resistance was performed only once per specimen.

The results of the water resistance measurements showed that 32 of the80 measurements did not produce a leak in 600 cycles, thus indicating arelatively high degree of water resistance. Five values fell below the100 cycle level, the lowest value being 71 cycles. Similar results wereobtained on eight of the sides whereas the other two showed asignificant difference in water resistance. The side with the lowestresistance had four forwater and gasoline resistance.

to several different liquid chemicals.

polysulfide-treated leather was tested against corrosive 'trol samples.

assent-s of its values below 100 cycles while the best side did not leakin any test.

In contrast to the above results, untreated leather permits waterpenetration in approximately 20 cycles.

A wet brick test was conducted on mittens fabricated from thepolysulfide-treated leather. In this severe test, the test subjecthandles wet bricks, lifting, turning and stacking them from a restingposition in'approximately one inch of water. The test subject detectedinitial water penetration in approximately 22 minutes on the average forthree mittens while untreated leather mittens took only an average of 30seconds. In less than minutes the untreated leather palm was saturatedwith water. In contrast the polysuliide-treated leather mittens retaineda dry, comfortable feel after 30 minutes, except for slight waterpenetration in isolated areas of the palm where the leather had beentightly squeezed against the wet bricks. The polysulfide-treated leathermittens were also found to be comparable to or better than untreatedleather in other water resistance properties, such as drying time andflexibility or softness after soaking.

Since the Water resistance characteristics of leather could be adverselyaffected by leaching or migration of the treating material during use,especially by repeated wetting and drying cycles, a severe test was madeon specimens from five of the ten sides of treated leather to determinethe permanency of the the treatment. The

leather specimens were subjected to a series of ten cycles of launderingand drying. In each cycle the leather speci- -mens were washed withlaundry soap for 15 minutes at 140 F., rinsed and dried at 140 F. for 30minutes. After the cycles the leather specimens were tested Allspecimens resisted water penetration for more than 600 cycles andtheyall received a rating of excellent in gasoline resistance. Thisshows the permanent characteristics of the treatment.

type liquids, such as battery acid (34 percent sulphuric acid),.2 Nsodium hydroxide, and liquids such as ethylene glycol. In eachdetermination, the liquid chemical was simply poured liberally onto thegrain surface of the'leather and permitted to stand for one hour.Comparison of the bursting strength property showed no loss in strengthfor the exposed and adjacent areas except in the exposure to the sodiumhydroxide solution.

'At room temperature and at -4i) F., the effect of the polysulfidetreatment on the stiifness characteristic of leather was measured withthe Tinius Olsen stillness tester and found to be not inferior to theuntreated con- Substantially the same results were obtained bysubstituting Thiokol LP-2 for Thiokol LP-32. ThiOkOl LP-2 has astructure and molecular Weight (about 4000) generally corresponding toThiokol LP-32, but is more crosslinked than Thiokol LP-32.

Example 11.

Cowhide glove leather was impregnated on the grain side with a solutioncomposed of Parts by weight Polysulfide polymer (Thiokol LP-32) M 64.3Tetrahydrofurfuryl alcohol 29 Morpholine 6.4 Oleic acid .3

For example, the

for one hour instead of 15 minutes. Most treated leather test specimensresisted water penetration for 600 cycles /2 pound load), or better, onthe Quartermaster tap tester.

The grain surfaces of sheepskin, deerskin and horsehide glove leatherswere also treated in accordance with the foregoing examples so as toreceive a concentration of about 15-18 grams of polymer per square footof leather. Water resistance values of 600 cycles or higher with aQuartermaster tap tester were observed.

Example" III The grain surface of cowhide upper leather was treated witha composition composed of liquid polysulfide poly mer 62.5 parts byweight, tetrahydrofurfuryl alcohol 31.25 parts by weight, morpholine6.25 parts by weight. A concentration of approximately 24-30 gramspolymer per square foot of leather grain surface was imparted Example IVThe grain surfaces of ten sides of cowhide glove leather were treated ina tannery with a composition of polysulfide polymer 77 parts by weight,and morpholine 23 parts by weight so as to receive a concentration of15-18 grams polymer per square foot of leather. The leathers weretreated by a swab technique ascommonly employed in the tannery. Afterapplication, the leather was heatcured at 140-160 F. for 16 hours andthen at -100 F. for 16-24 hours. The leathers were found by laboratoryevaluation to possess good resistance to penetration i water andpetroleum products. A field wear test with mittens fabricated from thistreated leather and similar butuntreated leather showed the untreatedmittens to absorb petroleum products at a rate nearly three times thatof the treated ones. After a 22-day test, the treated mittens were foundto be in a relatively dry condition as compared to the poor feel andappearance of the untreated ones. The test conclusions were that thetreated leather mittens would be considered satisfactory for resistingpetroleum products and that both types were adeto the grain side onlyresulted generally in leather either of poor liquid resistance or poorleather comfort characteristics. In contradistinction, our inventionpermits adequate impregnation of the leather from the grain side for thepurpose of achieving the intended objects of our invention.

Having thus described several practical examples of leather impregnationin accordance with our invention, ityvill be understood, of course, thatchanges and variations in procedural conditions may be made withoutdeparting from the spirit and scope of our invention. Thus, forinstance, liquid alkylene polysulfide partial polymers (i.e., liquidpolymers capable of further polymerization to form an elastomer) otherthan Thiokol LP-32 (which Was the Thiokol employed in Examples I to IVunless otherwise noted) may be used; or the curing at an elevatedtemperature non-injurious to the leather may be interrupted prior toelfecting a complete cure of the polysulfide partial polymer in theinter-fiber space of the leather, e.g., after about 15 minutes, so as topermit the cure to be completed at room temperature. We desire toencompass these and other variations and modifications within the scopeof our invention which we intend to claim broadly and. to this end haveappended the following claims. a s

We claim:

1. Method of treating leather, which comprises impregnating said leatherfrom the grain surface inwardly with a liquid composition comprisingfrom about 50 to about 80 parts by weight of a liquid alkylenepolysulfide polymer capable of being cured to form an elastomer, andfrom about 20 to about 50 parts by Weight of a member of the groupconsisting of tetrahydrofurfuryl alcohol, morpholine, and a mixture oftetrahydrofurfuryl alcohol and morpholine, and at least partially curingsaid composition in the interfiber space of said leather at atemperature above room temperature but non-injurious to said leather;whereby a flexible, liquid-resistant and cold-weather-resistantimpregnated leather is obtained.

2. The method according to claim 1, wherein said composition alsocontains from about A part to about 2 parts by weight of oleic acid.

3. Method of treating leather, which comprises impregnating said leatherfrom the grain surface inwardly with a liquid composition comprisingfrom about 50 to about 75 parts by weight of a liquid alkylenepolysulfide polymer capable of being cured to form an elastomer, andfrom about 25 to about 50 parts by weight of tetrahydrofurfuryl alcohol,and at least partially curing said composition in the interfiber spaceof said leather at a temperature above room temperature butnon-injurious to said leather, whereby a flexible liquid-resistant andcold-weather-resistant impregnated leather is obtained.

4. Method of treating leather, which comprises impregnating said leatherfrom the grain surface inwardly with a liquid composition comprisingfrom about 75 to 80 parts by weight of a liquid alkylene polysulfidepolymer capable of being cured to form an elastomer, and from about 20to 25 parts by weight of morpholine, and at least partially curing saidcomposition in the interfiber space of said leather at a temperatureabove room temperature but non-injurious to said leather; whereby aflexible liquid-resistant and cold-we'ather-resistant impregnatedleather is obtained.

5. Method of treating leather, which comprises impregnating said leatherfrom the grain surface inwardly with a liquid composition comprisingfrom about 50 to 80 parts by weight of a liquid alkylene polysulfidepolymer capable of being cured to form an elastomer, and from about 20to 50 parts by weight of a mixture of tetra- ,hydrofurfuryl alcohol andmorpholine, and at least parleather is obtained.

6. The method according to claim 1, wherein said liquid polymer has amolecular weight of about 1000 5000.

7. The method according to claim 1, wherein said liquid polymer hasa'viscosity of about 7 to about poises at 25 C.

8. The method according to claim 1, wherein said alkylene is C H 9. Themethod according to claim 1, wherein said curing temperature is about90-160 F.

10. Method of treating leather, which comprises impregnating saidleather from the grain surface inwardly with a liquid compositioncomprising from about to about 80 parts by Weight of a liquid alkylenepolysulfide polymer having a molecular weight of about 1000-5000 andcapable of being cured to form an elastomer, and

from about 20 to about 50 parts by weight of a member of the groupconsisting of tetrahydrofurfuryl alcohol, morpholine and a mixture oftetrahydrofurfuryl alcohol and morpholine, and at least partially curingsaid composition in the interfiber space of said leather at about 90-160F.; whereby a flexible, liquid-resistant and coldweather-resistantimpregnated leather is obtained.

11. The method according to claim 10, wherein said composition alsocontains from about A part to about 2 parts by weight of oleic acid.

12. A flexible, liquid-resistant and cold-weather-resistant impregnatedleather produced by the method of claim 1.

13. A liquid composition for impregnating leather, comprising from about50 to about 80 parts by weight of a liquid alkylene polysulfide polymercapable of being cured to form an elastomer, and from about 20 to about50 parts by weight of a member of the group consisting oftetrahydrofurfuryl alcohol, morpholine, and a mixture oftetrahydrofurfuryl alcohol and morpholine.

14. A composition according to claim 13, said composition alsocontaining from about A part to about 2 parts by Weight of oleic acid.

'15. A liquid composition for impregnating leather, comprising fromabout 50 to about 75 parts by weight of a liquid alkylene polysulfidepolymer capable of being cured to form an elastomer, and from about 25to about cured to form an elastomer', and from about 20 to about 25parts by weight of morpholine.

17. A liquid composition for impregnating leather,

comprising from about 50 to about parts by weightof a liquid alkylenepolysulfide polymer capable of being cured to form an elastomer, andfrom about 20 to about 50 parts by weight of a mixture oftetrahydrofurfuryl F alcohol and morpholine.

References Cited in the file of this patent UNITED STATES PATENTS

1. METHOD OF TREATING LEATHER, WHICH COMPRISES IMPREGNATING SAID LEATHERFROM THE GRAIN SURFACE INWARDLY WITH A LIQUID COMPOSISTION COMPRISINGFROM ABOUT 50 TO ABOUT 80 PARTS BY WEIGHT OF A LIQUID ALKYLENEPOLYSULFIDE POLYMER CAPABLE OF BEING CURED TO FORM AN ELASTOMER, ANDFROM ABOUT 20 TO ABOUT 50 PARTS BY WEIGHT OF A MEMBER OF THE GROUPCONSISTING OF TETRAHYDROFURFURYL ALCHOL, MORPHOLINE, AND A MIXTURE OFTETRAHYDROFURFURYL ALCOHOL AND MORPHOLINE, AND AT LEAST PARTIALLY CURINGSAID COMPOSITION IN THE INTERFIBER SPACE OF SAID LEATHER AT ATEMPERATURE ABOVE ROOM TEMPERATURE BUT NON-INJURIOUS TO SAID LEATHER,WHEREBY A FLEXIBLE, LIQUID-RESISTANT AND COLD-WEATHER-RESISTANTIMPREGNATED LEATHER IS OBTAINED.